Hi Gianluca,<br><br>Thanks for your information, That's great helpful. I decide to use a hardware local timer to record the beacon frames arrival time. After I looked close to the CACE AirPcap Classic wireless adapter, I found there are a AIROHA transceiver and a ZYDAS USB driver chip. Do you know where does the Winpcap implement the incoming packets filtering?<br>
<br>Cheers<br><br>John<br><br><div class="gmail_quote">2009/5/7 Gianluca Varenni <span dir="ltr"><<a href="mailto:gianluca.varenni@cacetech.com">gianluca.varenni@cacetech.com</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div bgcolor="#ffffff">
<div><font size="2"></font> </div>
<blockquote style="border-left: 2px solid rgb(0, 0, 0); padding-right: 0px; padding-left: 5px; margin-left: 5px; margin-right: 0px;"><div class="im">
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;">----- Original Message ----- </div>
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<b>From:</b>
<a title="locationdev@gmail.com" href="mailto:locationdev@gmail.com" target="_blank">John
Wang</a> </div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>To:</b> <a title="winpcap-users@winpcap.org" href="mailto:winpcap-users@winpcap.org" target="_blank">winpcap-users@winpcap.org</a> </div>
</div><div class="im"><div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>Sent:</b> Wednesday, May 06, 2009 6:36
AM</div>
<div style="font-family: arial; font-style: normal; font-variant: normal; font-weight: normal; font-size: 10pt; line-height: normal; font-size-adjust: none; font-stretch: normal;"><b>Subject:</b> Re: [Winpcap-users] Where does
the Winpcap timestampcomefrom?andothers</div>
<div><font size="2"></font><br></div></div><div><div></div><div class="h5">Hi,<br><br>I'm a little bit confused about
where exactly the arrival packets timestamps come from, in our first email,
you said:<br><br><span style="color: rgb(51, 51, 255);">"1. Where does the NPF
get the time information to timestamp these incoming packet? The time
information comes from a on board timer in the adapter or from a CPU or
similar computer clock?</span>
<div style="color: rgb(51, 51, 255);"><font color="#000000" size="2"></font> </div>
<div style="color: rgb(51, 51, 255);"><font size="2">--GV--</font></div>
<div><font style="color: rgb(51, 51, 255);" size="2">From the computer clock when
the packet gets delivered to WinPcap.</font><span style="color: rgb(51, 51, 255);">"</span><br><br><font color="#000000">I think that
means the timestamps come from computer timer, like CPU timer. But in you last
email, you said:<br><br><span style="color: rgb(51, 51, 255);">"</span></font><font style="color: rgb(51, 51, 255);"><font size="2">The only way to obtain that is to
have some device that timestamps packets in hardware. And even in that
case, most of the times the timestamps have microsecond precision (this is
what we have with the AirPcap adapters in hardware).</font></font><font color="#000000"><span style="color: rgb(51, 51, 255);">"<br><br><span style="color: rgb(0, 0, 0);">That sounds like, the AirPcap adapter has a timer
build in it, and the arrival packets timestamps come from this build in
timer.<br><br>So I want to get the confirmation from you, whether the arrival
packets are timestamped by the computer timer or the AirPcap adapter build in
timer.<br></span></span></font></div></div></div></blockquote>
<div><font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"><font size="2">In the case of the AirPcap adapters,
which are *custom* capture devices, we provide two timestamps: software based
ones and hardware based ones. The hardware based ones are generated by the
chipset itself and have microsecond precision.
</font></span></span></font></div>
<div><font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"></span></span></font> </div>
<div><font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"></span></span></font><font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"><font size="2">If
you use WinPcap on a standard network adapter (doesn't matter if it's wireless
or not), you just have software timestamps.</font></span></span></font></div>
<div><font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"></span></span></font> </div>
<div><font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"></span></span></font><font color="#000000" size="2"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);">Let me know if
this makes any sense to you.</span></span></font></div>
<div><font color="#000000" size="2"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"></span></span></font> </div>
<div><font color="#000000" size="2"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"></span></span></font><font color="#000000" size="2"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);">Have a nice
day</span></span></font></div><div class="im">
<div><font color="#000000" size="2"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"></span></span></font><font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"><font size="2">GV</font></span></span></font></div>
<font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);"><font size="2"></font></span></span></font>
<blockquote style="border-left: 2px solid rgb(0, 0, 0); padding-right: 0px; padding-left: 5px; margin-left: 5px; margin-right: 0px;"><font color="#000000"><span style="color: rgb(51, 51, 255);"><span style="color: rgb(0, 0, 0);">
<div><br>Cheers<br><br>John<br></div></span></span></font>
<p>
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